The diagnosis and/or treatment of disease in nuclear medicine constitute one of the major applications of short-lived radioisotopes. It is estimated that in nuclear medicine over 90% of the diagnostic procedures performed worldwide annually use 99mTc labelled radio-pharmaceuticals. Given the short half-life of radio-pharmaceuticals, it is helpful to have the facility to generate suitable radioisotopes on site. Accordingly, the adoption of portable hospital/clinic size 99mTc generators has greatly increased over the years. Portable radioisotope generators are used to obtain a shorter-lived daughter radioisotope which is the product of radioactive decay of a longer-lived parent radioisotope, usually adsorbed on a bed in an ion exchange column. Conventionally, the radioisotope generator includes shielding around the ion exchange column containing the parent radioisotope along with means for eluting the daughter radioisotope from the column with an eluate, such as saline solution. In use, the eluate is passed through the ion exchange column and the daughter radioisotope is collected in solution with the eluate, to be used as required.
In the case of 99mTc, this radioisotope is the principle product of the radioactive decay of 99Mo. Within the generator, conventionally the 99Mo is adsorbed on a bed of aluminium oxide and decays to generate 99mTc. As the 99mTc has a relatively short half-life it establishes a transient equilibrium within the ion exchange column after approximately twenty-four hours. Accordingly, the 99mTc can be eluted daily from the ion exchange column by flushing a solution of chloride ions, i.e. sterile saline solution through the ion exchange column. This prompts an ion exchange reaction, in which the chloride ions displace 99mTc but not 99Mo.
In the case of radio-pharmaceuticals, it is highly desirable for the radioisotope generator to be constructed and used under aseptic conditions i.e. there should be no ingress of bacteria into the generator. Moreover, due to the fact that the isotope used in the ion exchange column of the generator is radioactive, and is thereby extremely hazardous if not handled in the correct manner, the radioisotope generator also should be constructed and used under radiologically safe conditions.
In trying to ensure adequate radiological protection, some known radioisotope generators have tended to be of a complicated construction incorporating a large number of components and requiring the ion exchange column to be introduced early on in the construction of the generator. This means that there is a lengthy period during construction when the radioisotope generator and those constructing the generator are unnecessarily exposed to radiation. Such complex structures also add to the cost of the generator. It is thus important that the actual construction of the generator is reliable and limits the extent to which the generator and those constructing the generator are exposed to radiation during construction.
U.S. Pat. No. 3,946,238 describes a shielded radioisotope generator comprising a cylindrical shielded housing for a central repository. The repository is bound by a removable top cover and side walls and a base which are made from lead and which act as the shielding. Within the repository a bottle is provided which contains an ion exchange column on which 99Mo is absorbed. In this document the construction of the generator is almost completed before the ion exchange column is introduced to the repository. However, the eluate is introduced to/removed from the ion exchange column of the generator via apertures in the walls of the bottle. Thus, although the construction of the generator limits the exposure to radiation during construction, the eluate is introduced and extracted using only a pipette which is highly undesirable as it means that the users of the generator are exposed to radiation each time (i.e. once ever twenty-four hours) the radioisotope is extracted. Moreover, this arrangement provides no means for accurately controlling the flow of eluate.
U.S. Pat. No. 3,564,256 describes a radioisotope generator in which the ion exchange column is in a cylindrical holder which is located within two box-shaped elements that are in turn located within appropriate radiation shielding. The holder is closed by rubber plugs at both ends, and the box-shaped elements have passages opposite each of the rubber plugs in which respective needles are located. At the outermost ends of the needles quick-coupling members are provided to enable a syringe vessel containing a saline solution to be connected to one of the needles and to enable a collection vessel to be connected to the other of the two needles. It is self-evident that the box-shaped elements and the radiation shielding must be constructed around the holder containing the ion exchange column. Therefore, throughout the construction of the generator all parts of the generator and those constructing the generator will, of necessity, be exposed to radiation. Furthermore, although reference is made to needles being used to pierce the rubber plugs at each end of the holder, this generator construction provides no means for controlling the penetration of the needles through the plugs.
U.S. Pat. No. 4,387,303 describes a radioisotope generator comprising a column having an eluent inlet aperture and an eluate outlet aperture and containing an ion exchange bed with the parent radioisotope. Both the eluent inlet and eluate outlet are in communication with channels in the surrounding shielding for the introduction and removal of eluate to and from the ion exchange column. Although no information is provided with regard to the construction of the generator, it is evident that the shielding must be constructed around the ion exchange column as accurate alignment of the channels in the shielding with the inlet and outlet of the ion exchange column is essential. Thus, here too, during construction all parts of the generator and those constructing the generator will be exposed to radiation from the ion exchange column.
U.S. Pat. No. 4,801,047 describes a dispensing device for a radioisotope generator in which the vial containing the saline solution that will be used to flush out the desired radioisotope from the ion exchange column, is mounted in a carrier that is moveable relative to the hollow needle used to pierce the seal of the vial and to extract the saline solution. This construction is described as providing control of the amount of saline solution removed from the vial.